1. Field of the Invention
The present invention relates to a capacitor structure. In particular, the present invention relates to a capacitor structure for a pumping circuit.
2. Description of the Prior Art
In the conventional dynamic random access memory (DRAM) structure, the pumping circuit plays an essential role in generating high voltage for driving the cells for operation. With the progress of the technology of the DRAM, the workload of pumping circuits become heavier and heavier because the initial voltage (Vint) may drop to relatively low 1.0 V to 1.5 V when the voltage to drive the cells to operate remains at a relatively high voltage.
The pumping efficiency of the pumping circuit mainly lies in the value of the capacity in the pumping circuit. The greater the capacity, the greater the pumping efficiency and a higher output voltage may be provided. The value of the capacity usually depends on the contact area between the top electrode plate and the bottom electrode plate. How to increase the contact area between the top electrode plate and the bottom electrode plate becomes a crucial subject matter.
However, with the development of the technology of the DRAM, the allocation of the more and more limited spaces on the substrate becomes more and more critical. Because regular planar capacitors are employed in the conventional DRAMs, it greatly restrains the possibility from increasing the contact area between the top electrode plate and the bottom electrode plate. In order to thoroughly solve the problem that there is a gap between the operational voltage for driving the cells and the initial voltage, there is a need to come up with a solution to increase the contact area between the top electrode plate and the bottom electrode plate.